This invention relates to a power transmission belt adapted to transmit power from one pulley to another pulley. The invention is intended to overcome the difficulties inherent in a so-called "multi-V-belt" adapted to transmit large torques from a driving pulley to a driven pulley. The problems include vibration and turn-over thereof, which are often caused during the run. This invention also eliminates power transmission loss due to the non-uniformity in length of the belt elements forming the multi-V-belt, and increases the service life thereof.
In a conventional multi-V-belt drive system, a plurality of belts are laid over pulleys having a plurality of pulley grooves in such a manner that the belts engage the pulley grooves, respectively. Therefore, in the case where the multi-V-belt system is employed for driving a machine such as a crusher or a compressor which generates a relatively great impact load, the belts are liable to be vibrated separately and to be brought into contact with one another. As a result, the belts may be turned over, or come off the pulleys, and the belts may be prematurely damaged. A V-belt is driven through friction, and therefore it is necessary to apply a suitable tension to the belt before it is run. However, in the conventional multi-V-belt system, the belts are liable to be non-uniform in tension because as described above, the lengths of the belts are not uniform and as a result the belts are vibrated and the service lives thereof are shortened.
In order to overcome these difficulties, a power transmission belt has been proposed in the art, which is obtained by connecting the upper surfaces of individual V-belt bodies with a tie band formed with a wide cross angle fabric. Because the wide cross angle fabric is used, the belt is high in lengthwise stretchability, but it is low in widthwise stretchability because the angle in the widthwise direction is smaller. Accordingly, the belt cannot satisfactorily engage with the pulley, and the tie band is liable to peel off the belt. Thus, the proposed belt is still disadvantageous.
A power transmission belt using a nylon cord fabric as its tie band is also known in the art. This belt has excellent stretchability in the longitudinal direction. However, when the belt is used with a small diameter pulley, the rubber interposed between the cords of the cord fabric is excessively stretched, and accordingly the rubber is liable to be cracked. Since nylon cord fabric is used, the stretchability of the belt in the lateral direction is low, and therefore, the belt cannot suitably engage the pulley.